THE ANTI-PROLIFERATIVE AND ANTIOXIDANT ACTIVITY OF FOUR INDIGENOUS SOUTH AFRICAN PLANTS.

Background: Cancer is a major cause of death worldwide. Limitations of current cancer therapies necessitate the search for new anticancer drugs. Plants represent an immeasurable source of bioactive compounds for drug discovery. The objective of this study was to assess the anti-proliferative and antioxidant potential of four indigenous South African plants commonly used in traditional medicine. Materials and Methods: The anti-proliferative activity of the plant extracts were assessed by the 2,3-Bis-(2-Methoxy-4- Nitro-5-Sulfophenyl)-2H-Tetrazolium-5-Carboxanilide (XTT) assay on A431; HaCat; HeLa; MCF-7 and UCT-Mel 1 cells and sulforhodamine-B (SRB) assay on HCT-116 and HCT-15 cell lines. Antioxidant activity was determined using the 2, 2-diphenyl-1-picrylhydrazyl (DPPH), nitric oxide (NO) and superoxide scavenging assays. Results: Three of the plant extracts (Combretum mollefruit, Euclea crispa subsp. crispa leaves and stems and Sideroxylon inerme leaves and stems showed anti-proliferative activity on the A431 cells with IC50values ranging between 26.9 - 46.7 μg/ml. The Euclea crispa subsp. crispa extract also showed anti-proliferative activity on the MCF-7 cell line (45.7 μg/ml). All of the plant extracts (Combretum molle leaves and fruit, Euclea crispa subsp. crispa leaves and stems, Sideroxylon inerme leaves and stems and Terminalia prunioides leaves and stems) showed DPPH scavenging activity with IC50 values ranging from 1.8 μg/ml to 11.5 μg/ml. Conclusion: These results indicate that the active extracts of Combretum molle, Euclea crispa subsp. Crispa and Sideroxylon inerme warrants further investigation to determine the mechanism of anti-proliferative activity against cancerous cells. These plant extracts also show potential for further evaluation in the prevention and treatment of cancer

Induction of colon and cervical cancer cell death by cinnamic acid derivatives is mediated through the inhibition of Histone Deacetylases (HDAC)

<div><p>Recent studies from our group and many others have shown the ability of histone deacetylase (HDAC) inhibitors for retarding the growth of carcinomas of cervix, colon and rectum in vitro. A search for naturally occurring HDAC inhibitors continues due to the adverse effects associated with known HDAC inhibitors like SAHA and TSA. Therefore in the current study, naturally occurring cinnamic acids derivatives were screened for HDAC inhibitory effect using in silico docking method which identified cinnamic acids as potential candidates. Cinnamic acids (CA) are naturally occurring phenolic compounds known to exhibit anticancer properties. However, it is not clearly known whether the anticancer properties of CA derivatives are due to the inhibition of oncogenic HDACs, if so how the efficacy varies among various CA derivatives. Hence, the HDAC inhibitory potential of CA derivatives containing increasing number of hydroxylic groups or methoxy moieties was determined using Discovery Studio software and the most potent CA derivatives tested ex vivo (biochemical assay) as well as in vitro (using cell based assay). Among CA derivatives tested, dihydroxy cinnamic acid (DHCA, commonly known as caffeic acid) exhibited better interactions with HDAC2 (compared to other isoforms) in silico and inhibited its activity ex vivo as well as in vitro. Targeted reduction of HDAC activity using DHCA induced death of cancer cells by (a) generating reactive oxygen species, (b) arresting cells in S and G2/M phases; and (c) induction of caspase-3 mediated apoptosis. In conclusion, we demonstrated that DHCA inhibited cancer cell growth by binding to HDAC followed by the induction of apoptosis.</p></div

100μg of protein collected from DHCA treated (250, 750 and 1500μM) and untreated HCT-116 cells (48h) were subjected to western blot for estimation of p21 expression.

<p>The data revealed that DHCA induced the expression of tumor suppressor gene p21 and thus could inhibit the proliferation of cancer cells. The protein bands were quantified using image-J software and fold increase in expression plotted.</p

DHCA and sodium butyrate inhibited HDAC activity ex vivo: To assess whether DHCA (which showed better HDAC inhibition in silico) inhibits HDAC activity ex vivo, HDAC enzyme (isolated from HeLa cells-provided in kit) was incubated with increasing concentrations of DHCA for 20 minutes and the percentage inhibition calculated.

<p>Analysis of the data demonstrated much better HDAC inhibition with DHCA compared to sodium butyrate (a well-known HDAC inhibitor). TSA, another known HDAC inhibitor used as positive control in this study, showed much stronger HDAC inhibition compared to DHCA or sodium butyrate.</p

Docking energy and c-docker interactions of CA derivatives with HDAC at TSA binding site.

<p>Docking energy and c-docker interactions of CA derivatives with HDAC at TSA binding site.</p

Common- and IUPAC name of CA derivatives.

<p>Common- and IUPAC name of CA derivatives.</p

IC₅₀ values (in mM) of DHCA on colon and cervical cancer cell lines.

<p>IC₅₀ values (in mM) of DHCA on colon and cervical cancer cell lines.</p